Automatic generation of music is a relatively complex task, due to the difficulties associated with defining subjectively aesthetically pleasing factors in a way that enables a computer or the like to generate music. A simpler task is the production of chordal rhythmic accompaniment in real time, which has become a standard feature of many synthesizers. In its simplest form, such accompaniment involves interpreting chords or notes input by a user and generating a suitable accompaniment in the form of rhythmic chords or arpeggios.
An advanced system known as "EMI" uses augmented transition networks (ATMs), and is capable of producing relatively high quality works of music in the style of famous composers. EMI is based on a knowledge base of musical sequences known to be representative of a composer's work, which arc subsequently assembled using a musical grammar under the direction of a skilled human user. Unfortunately, the subjective quality of music generated by the EMI system is variable, and the system requires a great deal of skill on the part of the user to extract its full potential.